1. Field of the Invention
The present invention relates to a hybrid vehicle drive apparatus for driving a vehicle by both or any one of a driving force of an internal combustion engine and a drive force of an alternating current motor, and more particularly to a hybrid vehicle drive apparatus in which the alternating current motor is connected to a crank shaft between the internal combustion engine and a transmission.
2. Description of the Related Art
As a drive system for a hybrid vehicle, a system for driving a vehicle by both or any one of a drive force of an internal combustion engine and a drive force of an alternating current motor has been disclosed in Japanese Patent Application Laid-Open (JP-A) No. 9-156388. A stator employed in the alternating current motor for the hybrid vehicle is generally structured such that a multiplicity of ring-like silicone steel plates, each having a plurality of stator teeth protruding from an inner peripheral end portion of a ring-like stator core toward a center along a circumference, are laminated so as to constitute a stator core, and each stator coil is wound around the laminated portion of each stator tooth.
In order to improve a space factor of the stator coil wound around the stator tooth, it is desirable that the stator coil is closely wound around each of the stator teeth, and it is desirable that the stator coil is independently wound around each of the stator teeth. However, in the conventional stator shape, since the stator teeth are fixedly arranged adjacent to each other, it is impossible to closely wind the stator coil around each of the stator teeth with passing through a gap in each of the stator teeth, so that a high space factor cannot be obtained.
In order to solve the problem mentioned above, there can be considered a structure in which a stator core is constituted by arranging independent stator pieces corresponding to a predetermined angle (for example, corresponding to one slot) so as to form a ring shape, and a stator coil is wound around each of the stator pieces.
In general, in the case of fixing a steel stator to an aluminum motor housing, there is employed a fixing method utilizing the fact that a coefficient of thermal expansion of the aluminum is greater than a coefficient of thermal expansion of the steel. That is, an opening having an inner diameter slightly smaller than an outer peripheral size of the stator is formed at the aluminum motor housing, and the stator is press-fitted to the opening after the inner diameter of the opening is expanded by heating the motor housing.
However, in the structure in which the alternating current motor is arranged between the internal combustion engine and the transmission so as to be connected to the crank shaft as in the hybrid vehicle drive apparatus mentioned above, since the aluminum housing is heated in the same manner as in the case of fixing the steel stator to the aluminum housing due to the heat generated by the internal combustion engine during a driving operation of the vehicle a fitting state between both elements is loosened and the fixing method mentioned above canont be employed.
An object of the present invention is to provide a hybrid vehicle drive apparatus in which a stator of a motor used under a high temperature environment can be simply and securely fixed to a motor housing.
In order to achieve the object mentioned above, in accordance with the present invention, there is provided a hybrid vehicle drive apparatus in which an alternating current motor is connected to a crank shaft between an internal combustion engine and a transmission, wherein the alternating current motor is provided with a motor housing connected between an internal combustion engine housing and a transmission housing, a stator constituted by arranging a plurality of stator pieces so as to form a ring shape, a stator hold ring having an opening portion corresponding to an outer peripheral shape of the stator and structured such that the stator is press-fitted to the opening portion, and fixing means for fixing the stator hold ring to the motor housing, and wherein a coefficient of thermal expansion of the stator substantially coincides with a coefficient of thermal expansion of the stator hold ring.
In accordance with the feature mentioned above, since the coefficients of thermal expansion of the stator and the stator hold ring substantially coincide with each other, a looseness is not generated in the connecting portion between the stator and the stator hold ring even when the motor is heated due to the heat generated by the internal combustion engine during the driving operation of the vehicle. Since the stator hold ring and the motor housing are fixed by the suitable fixing means utilizing no thermal expansion and compression, it is possible to easily and securely fix the stator of the motor used under a high temperature environment to the motor housing.